Method and apparatus for forming a turbulizer

ABSTRACT

A turbulizer is formed that has corrugations that each have side walls with openings and offset portions in them. A strip is rolled longitudinally to form a corrugated strip that has longitudinally extending corrugations. Openings and the above-mentioned offset portions are formed in the corrugated strip. An apparatus for forming a turbulizer has one or more pairs of roll dies that have cooperating corrugated profiles that advance strip stock that is engaged between them. These roll dies provide the strip with longitudinally extending corrugations. First and second forming dies receive the corrugated strip and move relative to one another to form pairs of spaced cuts that each define a wall portion between them. This wall portion is displaced transversely of an adjacent portion of the corrugated strip. A fin or turbulizer for a heat exchanger has a strip that has longitudinally extending side edges and longitudinally extending corrugations. There are openings through the corrugations in a region that is intermediate the side edges. An imperforate side edge portion extends between the side edge and the intermediate region. The corrugations extend in a general plane. The imperforate side edge portion inclines with respect to that general plane outwardly away from the intermediate region. The side edge portion may incline with respect to the general plane outwardly away from the intermediate portion and may have a distal portion extending inwardly generally toward the intermediate portion.

This application claims priority to Canadian Patent Application No.2,431,732 filed Jun. 11, 2003.

The present invention relates to methods and apparatus for forming aninner fin or turbulizer, for example for a heat exchanger. Moreespecially the invention relates to forming turbulizers such as lowpressure drop turbulizers that are elongate and have corrugationsextending longitudinally of the turbulizer, and that may have openingsand offset portions formed in side walls of the corrugations. Further,the invention relates to novel fin or turbulizer structures that maypreferably be made using the above methods and apparatus.

It is known to form low pressure drop turbulizers by rolling or stampingstrip stock to form it with transverse corrugations. Since there arelimits on the widths of the strip stock that can be used, this places alimit on the length of the turbulizer that can be produced when it isdesired to employ an elongate turbulizer with longitudinal corrugationsas may be desired when the flow of fluid is parallel to the corrugationsto achieve a low drop in pressure.

In a first aspect, the present invention is directed to a method offorming a turbulizer having corrugations each having side walls withopenings and offset portions formed in said side walls, said methodcomprising:

-   -   (a) rolling a strip longitudinally to form a corrugated strip        having longitudinally extending corrugations; and    -   (b) forming said openings and said offset portions in said        corrugated strip.

The present invention is directed in a further aspect to an apparatusfor forming a turbulizer having corrugations each having side walls withopenings and offset portions formed in said side walls,

said apparatus comprising:

-   -   at least one pair of roll dies having cooperating corrugated        profiles adapted to advance strip stock engaged therebetween and        to provide it with longitudinally extending corrugations;    -   first and second forming dies adapted to receive said strip        having said corrugations exiting said at least one pair of roll        dies;    -   and said first and second forming dies on movement relative to        one another forming pairs of spaced cuts each defining a wall        portion between them and displacing each wall portion        transversely of an adjacent portion of said corrugated strip.

In a further aspect, the invention provides a fin or turbulizer for aheat exchanger comprising a strip having longitudinally extending sideedges and longitudinally extending corrugations, openings formed throughsaid corrugations in a region intermediate said side edges, animperforate side edge portion extending between said side edge and saidintermediate region, said strip having said corrugations thereinextending in a general plane, and said imperforate side edge portioninclining with respect to said general plane outwardly away from saidintermediate region.

In a still further aspect, the invention provides an inner fin orturbulizer for a heat exchanger comprising a strip having longitudinallyextending side edges and longitudinally extending corrugations, a sideedge portion extending inwardly from a side edge of the strip toward anintermediate portion thereof, said strip having said corrugationstherein extending in a general plane, and said side edge portioninclining with respect to said general plane outwardly away from saidintermediate portion and having a distal portion extending inwardlygenerally toward said intermediate portion.

The present invention will now be more fully described, by way ofexample only, with reference to the accompanying drawings. In theaccompanying drawings:

FIG. 1 is a partially schematic perspective view of one preferred formof apparatus for forming a turbulizer in accordance with the invention.

FIG. 2 is a side view of the apparatus of FIG. 1.

FIGS. 3 to 10 are end views of rolling die pairs taken on thecorrespondingly numbered section lines indicated in FIG. 1.

FIGS. 3 a to 10 a are cross-sectional views of the rolled strip profileachieved by the correspondingly numbered roll die pairs, respectively.

FIG. 11 is an end view taken from an end opposite to that of the view ofFIG. 1.

FIG. 12 is a partially schematic and fragmentary perspective view of theapparatus of FIG. 1 adjacent the exit end.

FIG. 13 is an exploded end view of the forming die portion of theapparatus, and showing the dies in open position.

FIGS. 14 and 15 are plan and end views, respectively, of a corrugatedstrip.

FIGS. 16 and 17 are plan and end views of a corrugated strip aftercutting and offsetting.

FIG. 18 is a partially fragmentary perspective view of a strip having aplain-corrugated portion and a cut and offset portion.

FIG. 19 is a partially schematic cross-section through the forming die,taken on the line 19-19 of FIG. 13, and showing the dies in closedposition.

FIG. 20 is a somewhat schematic perspective view of a die assemblyforming a portion of the forming die seen in FIG. 19.

FIGS. 21 to 23 are end views, similar to FIG. 17, of novel forms ofturbulizer that may be made using the method and apparatus of theinvention.

FIGS. 24 to 26 are cross sectional views through generally plate formheat exchangers incorporating the turbulizers of FIGS. 21 to 23,respectively.

Apparatus in accordance with the embodiment shown in the drawingcomprises a rolling station 26 wherein strip stock 27 is rolled to forma corrugated strip 28, a forming station 29 wherein the corrugated stripis formed with spaced cuts and portions between the cuts are offsetlaterally, and, in the example illustrated, a cutter station 31 whereinthe strip having openings and offset portions is cut into lengths.Stations 26, 29 and 31 may be supported on a common base 32.

The terms “transverse” and “laterally” have been used above, and it maybe clarified that the terms, and their derivatives, are used hereinthroughout in their ordinary meanings. “Transverse” is used herein torefer to directions that extend generally at right angles to thelongitudinal direction, and “lateral” to transverse directions thatextend generally parallel to the plane of the strip or to the corrugatedstrip.

In the example shown, station 26 consists of a series or train of rolldie pairs 33 through 40 shown in more detail in FIGS. 3 through 10. Eachroll pair 33 through 40 comprises an upper roll designated by suffix “a”and a lower roll designated by suffix “b”. Each roll is connected on arespective axle 42 journalled through conventional structure, not shown,that permits adjustment of the position of the associated roll, andparticularly with respect to the adjacent roll in its pair, to a pair ofsupport walls 43 connected to base 32.

A sprocket gear 44 is connected to each axle 42 and is engaged by aserpentine chain 46. The chain 46 is driven by a drive gear 47, andpasses over an idler gear 48. The chain 46 drives each roll incounter-rotation to the other roll in its pair. In use, the strip 27,drawn from a supply reel 51 and passing over an idler roll 52 is engagedbetween successive roll pairs 33 through 40 and is drawn therethrough.Adjacent its longitudinal median, each roll in the pairs 33 through 40has a peripherally continuous profile that imparts a corrugation orcorrugations to the strip 27 and provides the strip with a progressivelyincreasing number of corrugations transversely outwardly from itslongitudinal median. FIGS. 3 a to 10 a show the progressively morecomplex configurations, respectively, of the corrugated strip 28. Feweror greater numbers of corrugations may be imparted by adding or removingroll pairs. FIG. 1 shows eight roll pairs, and a roll pair has beenomitted between pairs 39 and 40. The corrugated strip 28 passes freelythrough the space between axles 42 in this region. Transverselyoutwardly from the corrugating profile, each roll has a cylindricalsurface that may lightly grip transversely outer margins of thecorrugated strip 28. The arrangement of the roll pair profiles is suchthat alternate roll pairs 33, 35, 37 and 39 have a corrugating profilecomprising a peripherally continuous recess within this surface on oneside (in the example shown the upper side) of the strip 28, and a rib orribs extending beyond this surface on the opposite or lower side. Eachother roll pair (34, 36, 38 and 40) has the opposite configuration, withribs on the said one (upper) side and a recess on the other, or lower,side. With each pass through a roll pair, this arrangement achieves agentle bending of the material transversely outwardly from and in adirection opposite to the bending achieved in the pass through thepreceding roll pair. The invention may subject the strip to less severeforming conditions than known methods, and relatively thin strip stockcan be corrugated without tearing of the material. For example, thestrip stock, which may for example comprise stainless steel or aluminum,may be about 0.05 to 2 mm thick, more preferably 0.1 to 0.5 mm thick.

In accordance with a preferred aspect of the present invention, multiplecorrugations are formed in strip stock by rolling in station 26.Portions of the corrugated strip are cut and offset at a subsequentstation 29 that in a preferred form comprises reciprocating stampingdies. Significant advantages accrue from this arrangement. Thecorrugating rolls entrain the strip stock and a separate strip stockfeeder is not required. Whereas stamping dies need to be large, massiveand relatively expensive in order to withstand the forces to which theyare subjected, the invention avoids use of large numbers of stampingdies and uses corrugating rolls that are of reduced size, cost andfootprint as compared with stamping dies.

In the preferred form as shown, chain drive gear 47 is rotated by aservo motor controlled by a controller operating the servo motor in acontinuously repeated cycle of operation, wherein firstly the motorturns the gear 47 through a predetermined angular rotation followed by apredetermined interval during which the gear 47 and chain 46 arestationary, following which the cycle of operation repeats bycommencement of turning of the motor and gear 47. As a result, the rollpairs rotate synchronously for intermittent periods during each of whichthe strip stock advances a predetermined length and a correspondinglength of corrugated strip stock 28 exits from between the last rollpair 40. Intermediate these intermittent periods there are rollstationary times of predetermined length during which the roll pairs andstrip 28 are stationary. During these roll stationary times, the formingstation 29 operates to provide cuts and offset portions in thecorrugated strip 28, to form an elongate turbulizer product.

FIGS. 14 and 15, for example, show a corrugated strip 28 having sevenraised corrugations 56. FIGS. 16, 17 and 18 illustrate a lanced andoffset strip 57 wherein cuts 58 have been made through substantially thefull height of each side wall of each corrugation and portions 59disposed between alternate adjacent pairs of cuts 58 have been offsettransversely of the original corrugations 56. The spaced cuts 58 in eachpair defining an offset portion 59 between them may be spaced uniformlylongitudinally apart in the product. At least over an extended portionof the length of the product, the pairs of spaced cuts may be spaceduniformly longitudinally apart. In FIGS. 16, 17 and 18, the spacingbetween adjacent cut pairs and offset portions 59 is substantially thesame as the spacing between cuts 58 in each pair.

While, as noted above, FIGS. 1 to 10 and 14 to 18 show by way of exampleforming a corrugated strip 28 having seven raised corrugations, it willbe appreciated that a strip having more or fewer corrugations may beformed employing a rolling station 26 having more or fewer roll diepairs 33 to 40. For greater clarity of illustration, the followingdescription of the operation of the forming station will refer to FIGS.12, 13, 19 and 20 that illustrate, merely by way of example, formingoperations conducted on a corrugated strip 28 having four raisedcorrugations. Similar apparatus to that illustrated, with minormodifications that will be readily apparent to those skilled in the art,may be used for corrugated strips having more or fewer corrugations andfor providing them with spaced cuts and offset portions as generallydescribed below.

In the example shown, a forming station 29 comprises a lower bolster 61mounted on base 32, and an upper bolster 62 reciprocating relative tolower bolster 61 in a direction indicated by arrow 60 transversely ofthe longitudinal path followed by strip stock 27 and by corrugated strip28. In the example illustrated, bolster 62 is connected to bushings 63sliding on dowels 64 connected to lower bolster 61. Support structure 66carries a fluid operated cylinder 67 having a piston working within itand connected to a piston rod 68. Rod 68 pivots at 69 to pivot structure71 pivoted to support structure 66 at 72. Link 73 is connected pivotallyat 74 and 76 to pivot structure 71 and to upper bolster 62,respectively. On extension of rod 68 from an “open” position shown insolid lines in FIG. 12, structure 71 rocks to a position moving link 73to a position in which upper bolster 62 is moved downwardly to a“closed” position shown in broken lines in FIG. 12. As will beappreciated by those skilled in the art, other means for moving theelements between open and closed positions may of course be adopted,such as air pressure operations, or a servomotor with an operating cam,and the like.

Lower and upper bolsters 61 and 62 carry first and second dies 77 and 78respectively. First die 77 comprises an assembly of a plurality oflongitudinal rows 79 of punches 81. In the example illustrated, each row79 includes a first series of punches 81 a that are aligned along afirst longitudinal axis and a second series 81 b that are aligned alonga second longitudinal axis that is offset laterally from the first axis.The punches 81 a are longitudinally spaced and alternate with punches 81b. Longitudinally opposing end faces 82 (see FIG. 20) of adjacentpunches in series 81 a and 81 b are in close proximity. The second dieassembly 78 has an arrangement of punches similar to and complementaryto the arrangement of the first die 77, so that when the dies 77 and 78close together, the punches 81 of the first die 77 inter engage snuglybetween the punches 83 of the second die 78. It will be noted that, inthe example shown in FIG. 19, the first die 77 comprises four rows ofpunches 81 a and 81 b. The second die 78 comprises five rows of punches83 cooperating with the punches 81 and 81 b of the lower die. In theexample illustrated, the punches 83 in the second die 78 include punches83 a that cooperate with, for example, punches 81 a of the first die 77,as seen in FIG. 19, and punches 83 b that cooperate with the punches 81b of the first die 77 and include a fifth row of punches 83 b seen atthe upper left hand side in FIG. 19 that cooperate with a laterallyoutermost punch 81 b and form the adjacent outer side of a corrugation.For clarity of illustration, not all of the punches 81 a, 81 b, 83 a and83 b are shown in FIG. 19. As will be appreciated, die configurationshaving more or fewer rows of punches may be adapted for differingconfigurations of corrugated strip.

In use, after each intermittent roll rotation period during which apredetermined length of the corrugated strip 28 has advanced from theexit end of the roll pairs, and while the rolls and strip 28 arestationary relative to the base 32, the controller actuates the cylinder62 to extend the piston rod 68 and close the dies 77 and 78 together onthe corrugated strip 28. As will be best appreciated from FIG. 19, ashearing action is exerted between opposing end faces 82 of adjacentpunches 81 of the first series 81 a and of the second series 81 b offsettherefrom, thereby forming cuts through the side walls of thecorrugations 56, while reaction between the punches 81 and 81 b of thefirst die 77 with the complementary punches 83 a and 83 b of the seconddie 78 cause portions 59 between adjacent pairs of cuts to be displacedor offset laterally.

The controller then operates to retract the rod 68 and disengage thedies 77 and 78 from the strip 57, and to commence rotation of the servomotor driving the drive gear 47. The cycle of operation thenre-commences.

In one mode of operation the length by which the strip 28 is advanced ineach intermittent roll rotation is substantially equal to thelongitudinal length of the dies 77 and 78 so that the product is formedwith cuts or openings and offset portions along substantially its entirelength. However, other modes of operation are possible, as discussedlater.

In order to assist in disengaging the punches 81 from the corrugated andlanced and offset strip 57, the laterally facing sides of the punches 81and 83 may have slight draft angles so that the punches 81 taperslightly toward their tip. Preferably, stripper plate arrangements areused to further assist in disengaging the punches of the dies 77 and 78from the strip 57. For example, a first stripper plate 86 has slots 87each of width and length sufficient to receive through it thelongitudinal rows 79 of the punches 81 of the first die 77. The plate 86forms part of an inverted tray-like structure 88 having downwardlydepending side walls and within which are received compression springs89 normally biasing the plate 86 upwardly to a position above the lowerbolster 61 and the punches 81 of the first die 77. The structure 88 isguided for vertical movement and limited in upward travel by guidestructure (not shown). A second stripper plate 91 that has slots 92 toaccommodate the rows of punches 83 in the second die 78 is connected oryoked to the first plate 86 by downwardly depending portions 93 securedto the plate 86. A recess 94 formed longitudinally through the portions93 is of dimensions sufficient to receive the width and depth of thecorrugated strip 28 and provides a guide through which the strip 28intermittently advances, and limits vertical or transverse deviation ofthe strip 28 laterally of its normal path of movement. At the limit ofupward travel of the plate 77, the recess 94 is aligned approximatelywith the line along which the rolls 40 a and 40 b of the final roll pair40 engage with the work piece or corrugated strip 28. Normally, theplates 86 and 91 are spaced from the dies 77 and 78 in the openposition. In operation, the punches 83 of the second die 78 penetratethe slots 92 as the die 78 moves to the closed position. The die 78engages the plate 91 and urges the plates 86 and 91 against the actionof the springs 89 to the fully closed position seen in FIG. 19 whereinthe punches 81 of the lower first die 77 penetrate the slots 87. Onopening of the dies, the plate 86 moving upwardly under the action ofsprings 89 disengages the lanced and offset strip 57 from the first die77 and secondly the plate 91 disengages the strip 57 from the second die78 following retraction of the latter beyond the upper limit of motionof the connected plates 86 and 91.

The compression of the corrugated strip 28 between the punches 81 and 83and the inner surfaces of the stripper plates 86 and 91 form the lancedand offset strip 57 to a desired size, and, in particular to a desiredheight dimension defined between a crest of a corrugation on one face ofthe strip 57 and a crest of a corrugation on an opposite face. As aresult the corrugated strips 57 can be manufactured using a relativelysmall number of roll die pairs as compared with methods that rely onrolling for control of the height dimension of the product.

The lanced and offset strip 57 exiting the forming station 29 may passthrough a conventional cutter device at station 31, for example aguillotine cutter or traversing cutter, that preferably operates underthe control of the controller to cut the strip into discrete lengthsduring roll stationary times As an alternative, the cutter may beincorporated in the dies 77 and/or 78, with a separate activation mode.By varying the timing of operation of the cutter, product of varyinglengths can be obtained.

A further advantage of the present method is that it providesconsiderable flexibility in the range of designs of fins or turbulizersthat can be produced.

For example, the procedure described above with reference to thedrawings may be easily modified to provide corrugations that vary inwavelength across the width of the corrugated strip 28, by adopting rolldie pairs of appropriate profile. In this manner it is possible toachieve a turbulizer having approximately planar portions, or portionsat least of relatively broadened channel width, that may beuninterrupted by lanced and offset corrugations, extending alonglongitudinal zones of the product. Such zones provide so-called “neutralchannels” described together with their advantages in commonly-assignedU.S. Pat. No. 6,273,183 (So et al) the disclosures of which areincorporated herein by reference.

While the example shown in the drawings has pairs of cuts spaceduniformly apart, with the cuts in each pair also spaced generallyuniformly, by simple modification of the arrangement of the punches 81and 83 these spacings can readily be varied as desired, and punches maybe omitted from portions of the dies corresponding to the abovementioned “neutral channel” zones, where desired.

Turbulizer strip comprising alternating lengths of fully formed regions,having spaced cuts and offset portions, and partially formed regions,that are corrugated only, can readily be achieved either by interruptingoperation of the forming station 29 periodically, or by overfeeding thestrip 28 by adopting a mode of operation in which the strip 28 isadvanced in each intermittent roll rotation a distance greater than thelength of the dies 77 and 78. The partially formed sections may beuseful with heat exchanger structures as pressure control zones.Moreover, it is often desired to cut holes through a turbulizer toaccommodate a heat exchanger design, especially at manifold locations.The partially formed portions facilitate hole cutting. Alternatively, ahole may be cut through a corrugated strip 28 before the strip 28 isprovided with spaced cuts and offset portions by passing it through theforming station 29, for example using hole punch operations at alocation between stations 26 and 29. A further preferred procedure forproviding holes is to pre-form holes in the starting material strip,such as a hole 96 indicated in broken lines in strip 27 in FIG. 1.

A still further advantage of the present method is that it readilyallows formation of fins or turbulizers having advantageously novel edgeprofiles, examples of which are illustrated in FIGS. 21 to 26.

FIGS. 21 to 23 show turbulizers 101 to 103, respectively, that each havemain or intermediate portions provided with corrugations 104 providedwith longitudinally spaced cuts and laterally offset portions 106.

It may be noted that the crests or channel bottoms of the corrugations104 are flattened. This may desirably be achieved by compression of thecorrugated strip with correspondingly profiled punches during a sizingor compression step performed within a recess such as recess 94 asdescribed above with reference to FIG. 19.

Each turbulizer 101 to 103 has a side edge portion 107 that inclinesoutwardly away from the corrugated intermediate region, at an angle withrespect to the general plane of the latter. Desirably, each edge portion107 is imperforate and is not provided with cuts or offset portions.

The side edge portions 107 of turbulizers 101 and 102 have distalportions 108 that extend inwardly generally toward the intermediate,corrugated portion, and that preferably curve smoothly from the mainportion of the edge portion 107 to its distal portion.

The side edge portions 107 of turbulizers 101 and 103 extend a distanceless than the height dimension of the turbulizer, i.e. the distancebetween a crest of a corrugation such a corrugation 104 on one face ofthe strip constituting the turbulizer, and a crest of a corrugation (orchannel base) such as corrugation 104a on an opposite face.

As will be readily understood by those skilled in the art, turbulizershaving profiles such as those shown for turbulizers 101 to 103 can beeasily manufactured employing conventional forming techniques to providethe edges of the corrugated strip 28 with the desired profiles,preferably by modified roll forming in the rolling station 26 before theforming station 29 and the modifications to the procedure describedabove with reference to FIGS. 1 to 20 do not need to be described indetail to allow one of ordinary skill in the art to carry out themodified process. For example, the inclining or inturned edges 107 and108 may be formed using profiled rollers engaging the edges of the strip28, the axes of the rollers inclining with respect to the general planeof the strip 28. It is also possible to form the edges of the corrugatedstrip to the desired profiles in a forming die for example in theforming station 29. The recess 94 may be dimensioned to provide aspacing between the side walls of the recess 24 and the laterallyoutermost punches 81 or 83 to accommodate and lightly engage the edgeportions 107.

FIGS. 24 to 26 show the turbulizers 101 to 103 disposed within brazedtogether generally channel section plate pairs 111 providing a fluidchannel in a heat exchanger component 112. The side edge portions 107accommodate tolerances in the gauge or width of the starting materialstrip 27 while avoiding defects or leaks in the assembled heat exchangercomponent. With known turbulizers, in the event that the product iswider than nominal or as designed, the edges may ride up the innersurfaces of the component 112 and interfere with assembly by insertionbetween the surfaces 113 to be brazed together or may prop the portionsapart. In the example of FIG. 24, an increase in the width of theturbulizer 101 results in increased width of the inturned distal portion108, without this increased width interfering with assembly or brazing.Similarly with the turbulizer 102, with the added advantage that thedistal portion 108, whether of nominal or increased width, can bond tothe adjacent inner surface of the plate 111, resulting in increasedefficiency of heat exchange. Likewise, the portion 107 of the turbulizer103 can accommodate increased width without risking an assembly defector leak.

Further, increased efficiency is achieved as compared with structures inwhich there is a gap between the edge of the turbulizer and the platepair channel. The structure extending into this gap avoids loss ofefficiency that results from the existence of a fluid bypass channel inthis gap, and provides for heat transfer augmentation. Moreover, fluidthat would otherwise bypass the intermediate portion of the turbulizertends to be deflected by the side edge portions 107 and 108 toward theintermediate portion that is provided with the heat exchange promotingspaced offset portions. Heat exchange efficiency is also increased as aresult of the increased surface area of the turbulizer.

1. Method of forming a turbulizer having corrugations each having sidewalls with openings and offset portions formed in said side walls, saidmethod comprising: (a) rolling a strip longitudinally to form acorrugated strip having longitudinally extending corrugations; and (b)forming said openings and said offset portions in said corrugated strip.2. Method according to claim 1 wherein said step of forming saidopenings and said offset portions in said corrugated strip comprisesforming pairs of spaced cuts extending transversely of said corrugatedstrip, each pair of spaced cuts defining a wall portion between them,and having each said wall portion displaced transversely of an adjacentportion of said corrugated strip.
 3. Method according to claim 2 whereinthe spaced cuts in each pair are spaced uniformly longitudinally apart.4. Method according to claim 2 wherein the pairs of spaced cuts arespaced uniformly longitudinally apart.
 5. Method according to claim 1wherein said openings and said offset portions are distributed uniformlycontinuously along said corrugated strip.
 6. Method according to claim 1wherein said openings and said offset portions are at differing spacingsalong said corrugated strip.
 7. Method according to claim 1 including astep of severing said corrugated strip transversely into discretelengths after said step of forming said openings and said offsetportions.
 8. Method according to claim 1 including providing first andsecond forming dies moving between an open position and a closedposition wherein the forming dies engage the corrugated strip betweenthem, said forming dies when moving to said closed position cooperatingto form said openings and said offset portions in said corrugated strip.9. Method according to claim 8 including providing at least one pair ofroll dies having cooperating corrugated profiles, said roll diesrotatingly driven during intermittent periods and having said stripengaged between said roll dies and said roll dies advancing said stripand providing it with corrugations by its passage between said rolldies, and including passing said strip having said corrugations betweensaid forming dies, and said forming dies moving intermittently to saidclosed position at roll stationary times intermediate said intermittentperiods.
 10. Method according to claim 8 including providing a train ofpairs of roll dies, each of said roll die pairs driven rotatinglysynchronously for intermittent periods that are intermediate rollstationary times and having said strip engaged and advanced successivelybetween pairs of roll dies of said train, said roll dies in each pairhaving cooperating corrugated profiles such that successive pairs ofroll dies form said strip with a progressively increasing number of saidcorrugations, and including exiting said strip from said train betweensaid forming dies, and wherein said forming dies move intermittently tosaid closed positions at said roll stationary times.
 11. Methodaccording to claim 1 wherein said strip has a thickness of 0.05 mm to 2mm.
 12. Method according to claim 11 wherein said thickness is 0.1 to0.5 mm.
 13. Apparatus for forming a turbulizer having corrugations eachhaving side walls with openings and offset portions formed in said sidewalls, said apparatus comprising: at least one pair of roll dies havingcooperating corrugated profiles adapted to advance strip stock engagedtherebetween and to provide it with longitudinally extendingcorrugations; first and second forming dies adapted to receive saidstrip having said corrugations exiting said at least one pair of rolldies; and said first and second forming dies on movement relative to oneanother forming pairs of spaced cuts each defining a wall portionbetween them and displacing each wall portion transversely of anadjacent portion of said corrugated strip.
 14. Apparatus according toclaim 13 including an operator device operated to move said first andsecond dies between an open position and a closed position engaging saidstrip; and including a drive rotating said roll dies during intermittentperiods that are intermediate roll stationary times; and wherein saidoperator device moves said first and second dies to said closed positionduring a roll stationary time, and said first and second dies on movingto the closed position are effective to form said pairs of spaced cutsand to displace each said wall portion transversely of an adjacentcorrugation portion.
 15. Apparatus according to claim 14 wherein saidfirst and second dies each have a longitudinal length and said drive iseffective to advance said strip stock a distance equal to saidlongitudinal length in successive intermittent periods.
 16. Apparatusaccording to claim 14 wherein said first and second dies each have alongitudinal length and said drive is effective to advance said stripstock a distance greater than said longitudinal length in successiveintermittent periods.
 17. Apparatus according to claim 14 wherein saidfirst and second dies each comprise at least one longitudinal row ofpunches each comprising a first series of longitudinally spaced punchesaligned to a first longitudinal axis, and a second series oflongitudinally spaced punches that are disposed alternately between thepunches of the first series, said punches in said second series alignedto a second longitudinal axis offset transversely from said firstlongitudinal axis, said punches of said first die generally opposing anddisposed complementarily with respect to said punches of said seconddie.
 18. Apparatus according to claim 17 wherein each of said first andsecond dies is provided with a respective stripper plate normallymaintained spaced from the die and having an elongated slot that ispenetrated by said at least one longitudinal row of punches in saidclosed position, and wherein said at least one pair of roll dies has aline of engagement of the rolls constituting said at least one pair, andsaid line of engagement is aligned with a region disposed between saidstripper plates in an open position.
 19. Apparatus according to claim 18including yoke structure yoking said stripper plates together. 20.Apparatus according to claim 19 including a biasing device biasing saidstripper plates normally a distance laterally away from each of saidfirst and second dies.
 21. Apparatus according to claim 19 wherein saidyoke structure provides laterally disposed guide surfaces adapted toguide said corrugated strip in its passage between said stripper plates.22. Apparatus according to claim 13 comprising a train of said pairs ofroll dies, said roll dies in each pair having cooperating corrugatedprofiles such that successive pairs form said strip with a progressivelyincreasing number of said corrugations.
 23. Apparatus according to claim13 including a cutter adapted to cut said strip exiting said formingdies into lengths.
 24. A fin or turbulizer for a heat exchangercomprising a strip having longitudinally extending side edges andlongitudinally extending corrugations, openings formed through saidcorrugations in a region intermediate said side edges, an imperforateside edge portion extending between said side edge and said intermediateregion, said strip having said corrugations therein extending in ageneral plane, and said imperforate side edge portion inclining withrespect to said general plane outwardly away from said intermediateregion.
 25. A fin or turbulizer according to claim 24 wherein said striphaving said corrugations therein has a height dimension defined betweena crest of a corrugation on a face of said strip and a crest of acorrugation on an opposite face of said strip, and wherein said sideedge portion extends a distance less than said height dimensions.
 26. Aninner fin or turbulizer for a heat exchanger comprising a strip havinglongitudinally extending side edges and longitudinally extendingcorrugations, a side edge portion extending inwardly from a side edge ofthe strip toward an intermediate portion thereof, said strip having saidcorrugations therein extending in a general plane, and said side edgeportion inclining with respect to said general plane outwardly away fromsaid intermediate portion and having a distal portion extending inwardlygenerally toward said intermediate portion.
 27. A fin or turbulizeraccording to claim 26 wherein said side edge portion curves smoothlytoward said distal portion.
 28. A fin or turbulizer according to claim26 wherein said strip having said corrugations therein has a heightdimension defined between a crest of a corrugation on a face of saidstrip and a crest of a corrugation on an opposite face of said strip,and wherein said side edge portion extends a distance less than saidheight dimensions.